A total of 40 implants were installed (ICI implant, Galimplant, Sarria, Spain), with 3.5 mm in diameter by 10 mm in length. Eight implants in each dog, half per hemimandible. The surface treatment of this implant model is developed by blasting with three different granulometries of Al₂O₃ and pickling using a hydrofluoric solution (HF) at low temperature and short time, which aims to remove any traces of Al₂O₃. Plus, the conditioning of the surface was performed using hydrochloric acid solution (HCl) and sulfuric acid (H₂SO₄) at high temperature and short time (Fig. 1). Twenty titanium healing abutments with 3.5 mm in diameter and 6 mm in length were used.

Five American foxhound dogs of approximately 1 year of age were used in this study. The Ethics Committee for Animal Research at The University of Murcia (Spain) approved the study protocol, which followed the guidelines established by the European Union Council Directive of February 2013 (R.D.53/2013). Clinical examination determined that all animals were in good general health; moreover, all animals presented intact maxillae, without occlusal trauma or mucosal lesions.

The animals were pre-anesthetized with acepromazine 0.12–0.25 mg/kg, buprenorphine 0.01 mg/kg, and medetomidine 35 mg/kg. This mixture was injected intramuscularly in the femoral quadriceps. Animals were then taken to the operating theater, where an intravenous catheter was inserted into the cephalic vein, and propofol (0.4 mg/kg/ min) was continuously infused to maintain the general anesthesia. Conventional dental infiltration anesthesia (articaine 40 mg, 1% epinephrine) was injected at the surgical intraoral sites. All procedures were carried out under the supervision of a veterinary surgeon.

Initially, an impression of each hemimandible was performed to make a surgical guide indicate the implant position, which was predetermined to correspond with the distal root and the center of the crown teeth. Sixty days previous to the surgery, the left mandibular premolars (P2, P3, P4) and molar (M1) were extracted to heal the alveolus sites [21]. In the surgery to place the implants, equally to previous surgery, the teeth of the right hemimandibles were sectioned in a bucco-lingual direction using a tungsten carbide bur so that the roots could be extracted individually without damaging the remaining bony walls. After that, full-thickness mucoperiosteal flaps were increased. The socket of the distal root of each premolar was used as experimental site. For the left sides, a full-thickness mucoperiostal flap was used. All implants were positioned in the crestal bone level. After implant placement, a randomization (randomization.com) was performed to determine which implants received healing abutment and the submerged implants, forming four groups: implant installed in fresh extraction and submerged (group 1), implants in fresh extraction and immediately exposed (group 2), implants installed in healed site and submerged (group 3), and implants in healed site and immediately exposed (group 4). The height of the healing abutments was determined to stay 0.5 mm less of the contact with the corresponding antagonist teeth. No grafting materials were used between the implants and the bony plates. The flaps were closed using single nonabsorbable sutures (Silk® 4-0, Sweden & Martina, Due Carrare). After the surgical procedures, animals received antibiotic treatment (amoxicillin 500 mg, twice a day) and analgesics (ibuprofen 600 mg, three times a day) via the systemic route. Moreover, dogs were fed a soft diet for 7 days, and plaque control was maintained by the application of Sea 4 (Sea 4 teeth, Blue Sea Laboratories, Alicante, Spain). Wounds were inspected daily for clinical postsurgical complications. Two weeks after surgery, sutures were removed. All animals were sacrificed at 12 weeks after the implant insertion by means of an overdose of Pentothal Natrium® (Abbott Laboratories, Madrid, Spain).